The present invention is related to communication systems, and more particularly to a communication system interconnecting data transmitting and receiving units by infrared signals, and to a method of transmitting data in a system comprising a plurality of units including stations and associated devices.
The use of infrared signals for exchanging information between devices has received increased interest during recent years. The advantage of such systems is the elimination of special signal transmitting media such as wires. With respect to radio frequency (RF) transmission, infrared (IR) transmission has the advantages that no communication regulations apply and no PTT or FCC license is required, no disturbance by EMI and no interference from other RF channels can occur, and the radiation is confined to a room so that better data security is available than with RF systems.
Several IR transmission systems were described in the literature and disclosed in patents.
An article by F. Gfeller and U. Bapst entitled "Wireless In-House Data Communication via Diffuse Infrared Radiation", published in Proceedings of the IEEE, Vol. 67, No. 11, Nov. 1979, pp. 1474-1486 describes a communication network in which data are transferred between a plurality of terminals and a host computer. Each room in which terminals are located comprises a satellite station which receives IR signals from and distributes IR signals to the terminals. All satellites are connected to the host by an electrical wire network. No direct communication between terminals is provided.
In U.S. Pat. No. 4,402,090 entitled "Communication System in which Data are Transferred Between Terminal Stations and Satellite Stations by Infrared Signals", as well as in an article by F. Gfeller "Infranet: Infrared Microbroadcasting Network for In-House Data Communication", published in Proceedings, 7th European Conference on Optical Communications, Sept. 1981, pp. P27-1 -P27-4, a similar system is described which however provides a plurality of satellite stations for a large room to enable coverage of the larger area which is not possible with a single satellite. Though this prior art solves the problem of possible multiple reception of the same message via the IR channel, it does not provide for direct communication between the terminal stations.
With the rapidly increasing number of intelligent workstations and personal computers in all areas of business, administration, etc. there is also an increasing need for connecting I/O devices such as keyboards, displays, printers to them, and for interconnecting such workstations and small computers to each other. The use of electrical wire networks becomes a problem in particular with high density of stations and in the many cases where the location of stations or the configuration of subsystems must be changed frequently. It is therefore desirable to use IR signal transmission for interconnecting such devices and workstations to eliminate the requirement of electrical cable networks.
A problem, however, is the possible mutual interference of infrared signals if several connections are to be maintained simultaneously which is necessary e.g. in a large office environment. Frequency multiplexing is not possible because there is not enough bandwidth so that all devices must use the same baseband channel.